Part One - Background information

Today we will be observing an organism classified as a protist. A protist is any eukaryote that cannot be classified as a plant, animal, or fungus. There are several types of protists. We will be learning about three types of protists: protozoans, algae, and decomposers. In this lab you will be observing a type of protist called a protozoan. A protozoan is a protist that is similar to an animal. All protozoans are heterotrophs and hunt or search for their food.

One way protozoans are classified into groups is by how they move. In general, there are three ways protozoans move: by pseudopods, by cilia, or by flagella.

The protozoa you will observe today is called the amoeba. An amoeba is unicellular and moves by using pseudopods. A pseudopod is a temporary bulge that forms in the cell membrane as a result of the movement of the cytoplasm. The word pseduopod means "false foot." The pseudopod has two functions, or uses: 1. to move, 2. to capture food. The picture below shows an example of a pseudopod in an amoeba. (Note: in the picture the cytoplasm is called the "plasmasol" and the cell membrane is called the "plasma membrane.") Because the amoeba uses pseudopods to move and capture food, it is classified as a sarcodine. A sarcodine is a protozoan that uses pseudopods.

Example of a pseudopod in an amoeba. Source: http://www2.estrellamountain.edu/faculty/farabee/biobk/BioBookDiversity_3.html

Part Two - Observing movement

The video below shows how the amoeba moves. Again, the amoeba moves by using its pseudopods. By pushing the cytoplasm in one direction, it forces the cell to move into that direction.

Observe the movement of the amoeba in the video below. Draw what it looks like at 0 seconds, 15 seconds, and 30 seconds. Draw an arrow on each of your pictures indicating where the cytoplasm is moving.

Draw your observations of the amoeba at 15 sec intervals from the video below.

Part Three - Cell Structures

The amoeba has many easily identified parts. First, locate the nucleus. It is circular in shape, darker in color, and appears to have a rough surface. Just as in other cells we have studied, the nucleus is the control center of the cell; it contains the genetic information (DNA). You should also be able to see another large, clear circle (on the left). This is the contractile vacuole. The contractile vacuole collects water that enters the cell from osmosis. It temporarily stores water before removing it from the cell. Observing a live specimen, you can see the contractile vacuole expand and contract as it fills with and removes water!

You'll also be able to observe food vacuoles. The food vacuoles store food particles for the amoeba. In the picture below, they appear in a greenish color. The green organisms that the amoeba fed on are called chlorella. The outer part of the amoeba is the cell membrane.